In general, producers of coatings, paints, adhesives, and related products have preferred solvent borne systems instead of water borne systems because solvent borne systems allegedly exhibit superiority in properties such as film forming, water resistance, hardness, and freeze-thaw stability. Waterborne systems, however, are more environmentally friendly than solvent borne systems.
Current regulatory trends that seek to reduce the amount of volatile organic components (VOC's) released into the environment are causing a shift in favor of water borne systems. Recent regulations mandating the reduction of VOC's have made it increasingly difficult to achieve desired properties such as block resistance, adhesion, optical clarity, gloss, pigment dispersion, blister resistance, minimum film-forming temperature, and freeze-thaw stability. As a result, even though water borne systems, such as those containing emulsion polymer latexes, are used as alternatives to solvent based systems, there is still a great need for improved emulsion polymer latexes as a component therein. There is also a need for improved water borne systems utilizing such emulsion polymer latexes.
Surfactants play a crucial role in the formation of emulsion polymer latexes. Once the latex has been made, surfactants that remain can be detrimental in subsequent steps of fabrication, or in the final application. Some examples of these deleterious effects are surfactant blooming or surfactant blushing. Surfactant blooming, or blushing, occurs when a film is contacted with water and the surfactant migrates. This can result in the film becoming hazy.
It is also generally thought that too much surfactant typically results in low water resistivity. Problems associated with surfactants may also arise from the post-polymerization mobility of the surfactants. For instance, the surfactant could migrate from the surface of latex particles to the liquid-air interface or from the surface of a formed latex film. Systems are thus needed that minimize the adverse effects of surfactants in water borne emulsion polymer latex applications.
One way in which latex manufacturers address the problems associated with residual surfactants is through the use of low molecular weight polymers that are compatible with latex and act as emulsion stabilizers. Such low molecular weight polymers are typically polyelectrolytes that have molecular weights of between 1000 and 5000 g/mole and acid values between 140 and 300 mg KOH/g.
Other attempts to minimize the adverse effects of surfactants in emulsion polymer applications have resulted in surfactants that are designed to incorporate within latex through covalent bonds, or through a combination of covalent and ionic interactions. Such polymerizable surfactants include surfmers and non-migrating surfactants.
Current methods of attempting to mitigate the problems associated with residual surfactants, such as those described above, can present difficulties in handling and formulation. There remains a need for alternative environmentally friendly systems that mitigate the problems associated with surfactants due to the post-polymerization mobility of the surfactants while providing increased water resistance and improvements in block resistance, adhesion, optical clarity, and freeze-thaw stability.